Earnings Per Share (Computation of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net income	$ 9,334	$ 11,164	$ 6,592	$ 17,751	$ 36,638	$ 12,824	$ 11,029	$ 13,142	$ 44,841	$ 73,633	$ 45,404
Weighted average common shares									47,206,669	46,669,440	46,132,389
Stock-based awards									838,415	1,106,262	1,184,149
Weighted average common shares assuming dilution									48,045,084	47,775,702	47,316,538
Earnings (Loss) Per Share, Basic and Diluted [Abstract]
Basic earnings per share	$ 0.20	$ 0.24	$ 0.14	$ 0.38	$ 0.78	$ 0.27	$ 0.24	$ 0.28	$ 0.95	$ 1.58	$ 0.98
Diluted earnings per share	$ 0.19	$ 0.23	$ 0.14	$ 0.37	$ 0.76	$ 0.27	$ 0.23	$ 0.28	$ 0.93	$ 1.54	$ 0.96
Shares excluded from calculations of diluted earnings per share									48,881	4,634	7,339